1. Technical Field
The present disclosure relates to an ultrasonic flowmeter transducer, and more particularly, to an ultrasonic flowmeter transducer capable of being attached to a pipe and operating under extreme temperature conditions.
2. Discussion of Related Art
The use of a pipe wall as an ultrasonic flowmeter transducer, by exciting the natural waveguide mode of operation in the pipe wall, has been the basis of non-intrusive liquid and gas flowmeters and is referred to herein as the WideBeam technique. The use of a pipe wall as an ultrasonic flowmeter transducer, that is the WideBeam technique, is described, for example, in U.S. Pat. No. 6,062,091 to Baumoel, entitled “Method And Apparatus For Determining Ultrasonic Pulse Arrival In Fluid Using Phase Correlation,” which is commonly owned and incorporated herein by reference.
In general, ultrasonic energy can be used to determine flow velocity through a pipe by determining the effect of fluid flow on an ultrasonic signal passing through the fluid in the pipe. Ultrasonic flow metering can be performed without requiring intrusion into the pipe by clamping transmitting and receiving transducers onto the pipe and injecting ultrasonic signals through the pipe wall.
To excite this mode of operation, an external ultrasonic transducer can be clamped onto the pipe. The external transducer develops the necessary frequency and phase velocity to match the waveguide properties of the pipe, which depend on the material and the wall thickness of the pipe. Known methods of mounting and clamping external transducers to pipes are described, for example, in U.S. Pat. No. 6,405,603 to Baumoel, entitled “Method For Determining Relative Amounts Of Constituents In A Multiphase Flow,” and U.S. Pat. No. 6,418,796 to Baumoel, entitled “Sonic Flow Measurement Apparatus For Tubes Including Sonically Matched Plates,” which are commonly owned and incorporated herein by reference.
For example, a clamp-on wide beam ultrasonic flow meter can include a pair of ultrasonic transducers, which are clamped to the exterior of a pipe so as to inject sonic energy into the pipe. In accordance with the wide sonic beam principle, sonic energy from a first transducer is injected into the pipe wall. The sonic energy in the form of a wide beam is injected in the pipe in a way which excites a natural mode of sonic transmission of the pipe. In this way, sonic waves travel down the pipe and are measured by a second transducer. The sonic wave travels down the pipe wall at a velocity characteristic of the pipe's material, and at a frequency dependent on the pipe material and a wall thickness.
As the wave travels down the pipe wall, it radiates a sonic wave into the fluid flow, which ultimately reenters the pipe wall on the same side of the pipe from which it was originally transmitted and then enters the second transducer, wherein sonic energy is output as a receive signal. The receive signal is influenced by the flow through which the wave has passed.
A clamp-on transducer should be made from a material with a sonic propagation velocity considerably lower than that of the pipe material so as to develop the necessary phase velocity. Materials known to have such a velocity are, for example, plastics. Such materials, however, do not have the capability of surviving or functioning for requisite periods of time at temperatures encountered in such applications as steam or very high temperature water, as used in power applications.
Accordingly, means must be developed by which the high performance capability of the WideBeam technique can be extended to very high temperature applications, or to very low temperatures, such as those encountered in cryogenic applications.